1. Field of the Invention
The present invention is related to an ophthalmologic apparatus that includes an ocular fundus tracking controller for detecting a direction of gaze of an examined eye and following an ocular fundus imaging system in the direction of gaze, thereby photographing an ocular fundus with high resolution.
2. Description of the Related Technology
A conventional ocular fundus camera produces a deterioration in an ocular fundus image photographed because of optical aberration owned by the tested eye. Accordingly, the ocular fundus camera has an disadvantage that an clear image of the ocular fundus having high magnification cannot be obtained.
Owing to this, these days, a technology for photographing an ocular fundus image is proposed by which the optical aberration of the tested eye is measured and compensated by using a compensation optical system based on the measured results. The technology can eliminate an influence caused by the optical aberration of the tested eye to produce a higher magnification of the ocular fundus image compared with the conventional technique.
However, the conventional ophthalmologic apparatus has difficulties in photographing an ocular fundus image with much higher magnification and higher resolution applied to a visual cell level. One of the difficulties is a fixation micro-movement of an eyeball.
That is, the eyeball always continues a micro-movement called a fixation micro-movement, which always moves a gaze direction of the eye. Accordingly, since an ocular fundus image to be photographed is oscillating and causes a blur, it is essential to remove an influence of the fixation micro-movement in order to take a picture of the ocular fundus image with much higher resolution.
So as to get rid of the blur of the ocular fundus image in a difference of the gaze direction of the eye, an ophthalmologic apparatus has been proposed in which the gaze direction of the examined eye is detected and tracking is carried out with respect to the ocular fundus based on the detection results. See, for example, U.S. Pat. No. 5,943,115.
According to the technology disclosed in the US patent, in order to detect a gaze direction of the tested eye on the ocular fundus, a detection beam of a infinitesimal region close to the point light source is projected to the ocular fundus so that a circular locus is drawn on the ocular fundus by using a pair of oscillatory reflective mirrors, and then the ocular fundus is scanned. A reflective beam derived from the scanned beam and reflected on the ocular fundus is measured, which detects the gaze direction of the examined eye.
That is, when the scanned regions for the detection beam, which is projected on the ocular fundus, are varied owing to a change in the gaze direction, a light quantity signal of the reflected beam produced by the scanning of the detection beam is also varied due to a difference in a reflective index of the ocular fundus. Paying attention to the point, the technology of the patent detects the gaze direction of the tested eye from a varied quantity of the reflected light quantity to perform a tracking control over the ocular fundus based on the detected results.
On the other hand, in order to detect the gaze direction of the tested eye, the technology of the patent requires projecting on the ocular fundus the detection beam with a spot-like infinitesimal region and scanning the detection beam on the ocular fundus. Therefore, it is essential to detect the spot-like reflected light only. There is a need for a ophthalmologic apparatus that can solve the situation.